Biomedical Engineering Department, Northwestern University, Evanston, Illinois, United States of America.
PLoS One. 2013 May 28;8(5):e64600. doi: 10.1371/journal.pone.0064600. Print 2013.
Normal cell function is dependent on the proper maintenance of chromatin structure. Regulation of chromatin structure is controlled by histone modifications that directly influence chromatin architecture and genome function. Specifically, the histone deacetylase (HDAC) family of proteins modulate chromatin compaction and are commonly dysregulated in many tumors, including colorectal cancer (CRC). However, the role of HDAC proteins in early colorectal carcinogenesis has not been previously reported. We found HDAC1, HDAC2, HDAC3, HDAC5, and HDAC7 all to be up-regulated in the field of human CRC. Furthermore, we observed that HDAC2 up-regulation is one of the earliest events in CRC carcinogenesis and observed this in human field carcinogenesis, the azoxymethane-treated rat model, and in more aggressive colon cancer cell lines. The universality of HDAC2 up-regulation suggests that HDAC2 up-regulation is a novel and important early event in CRC, which may serve as a biomarker. HDAC inhibitors (HDACIs) interfere with tumorigenic HDAC activity; however, the precise mechanisms involved in this process remain to be elucidated. We confirmed that HDAC inhibition by valproic acid (VPA) targeted the more aggressive cell line. Using nuclease digestion assays and transmission electron microscopy imaging, we observed that VPA treatment induced greater changes in chromatin structure in the more aggressive cell line. Furthermore, we used the novel imaging technique partial wave spectroscopy (PWS) to quantify nanoscale alterations in chromatin. We noted that the PWS results are consistent with the biological assays, indicating a greater effect of VPA treatment in the more aggressive cell type. Together, these results demonstrate the importance of HDAC activity in early carcinogenic events and the unique role of higher-order chromatin structure in determining cell tumorigenicity.
正常细胞功能依赖于染色质结构的正确维持。染色质结构的调节受组蛋白修饰的控制，这些修饰直接影响染色质结构和基因组功能。具体来说，组蛋白去乙酰化酶（HDAC）家族蛋白调节染色质的紧缩，并且在包括结直肠癌（CRC）在内的许多肿瘤中通常失调。然而，HDAC 蛋白在结直肠早期癌变中的作用尚未得到报道。我们发现 HDAC1、HDAC2、HDAC3、HDAC5 和 HDAC7 在人类 CRC 的肿瘤组织中均上调。此外，我们观察到 HDAC2 的上调是 CRC 癌变过程中的最早事件之一，并且在人类癌前病变、氧化偶氮甲烷处理的大鼠模型和侵袭性更强的结肠癌细胞系中也观察到了这一点。HDAC2 上调的普遍性表明，HDAC2 上调是 CRC 中的一个新的重要早期事件，它可能作为一种生物标志物。组蛋白去乙酰化酶抑制剂（HDACIs）干扰致瘤性 HDAC 活性；然而，这一过程中涉及的确切机制仍有待阐明。我们证实，丙戊酸（VPA）通过抑制 HDAC 来靶向更具侵袭性的细胞系。通过核酸酶消化实验和透射电子显微镜成像，我们观察到 VPA 处理在更具侵袭性的细胞系中诱导了更大的染色质结构变化。此外，我们使用新的成像技术部分波谱（PWS）来定量染色质的纳米级变化。我们注意到，PWS 的结果与生物测定结果一致，表明 VPA 处理在更具侵袭性的细胞类型中具有更大的效果。综上所述，这些结果表明 HDAC 活性在早期致癌事件中的重要性以及高级染色质结构在决定细胞致瘤性方面的独特作用。
